Automatic carburetor choke control



y 8, 1953 L. D. BOYCE 2,646,933

AUTOMATIC CARBURETOR CHOKE CONTROL Original Filed May 9, 1947 INVENTOR.LEONARD D. BOYCE ATTORNEY Q Patented July 28, 1953 AUTOMATIC CARBURETORCHOKE CONTROL Leonard D. Boyce, Kirkwood, Mo., assignor to CarterCarburetor Corporation, St. Louis, Mo., a corporation of DelawareOriginal application May 9, 1947, Serial No.

747,029, now Patent No. 2,533,551, dated December 12, 1950. Divided andthis application September 22, 1950, Serial No. 186,286

4 Claims. 1

This invention relates to carburetors for internal combustion engines ofthe automotive type and consists particularly in a novel automatic chokecontrol therefor. This application is a division of my copendingapplication, Serial No. 747,029, filed May 9, 1947, now Patent No.2,533,551 of December 12, 1950.

The present, generally used type of automatic choke control forautomotive carburetors utilizes a bi-metal coiled spring which expandswhen the temperature is low to urge the unbalanced butterfly choke valveclosed. Since the thermostat is mounted on the carburetor air horn at apoint remote from the engine and, particularly the intake manifoldthereof, there is a tendency for the thermostat to cool quicker than theengine. Thus, if the engine is stopped before it is fully heated and anattempt is made to restart it within a few minutes, more closing forcemay be applied to the choke than is desirable to obtain the propermixture corresponding with the existing engine temperature. Accordingly,the mixture would be too rich and restarting impeded.

An object of the present invention is to provide means for counteractingthe portion of the thermostat action which, at low temperatures, effectsthe final closing movement of the choke valve.

Another object is to avoid the premature or excessive closing of thechoke valve due to excessive cooling of the thermostat, as explainedabove.

These objects and other more detailed objects hereafter appearing areattained by the device illustrated in the accompanying drawings inwhich:

Fig. 1 is a side view and section showing the upper part of a carburetorand automatic choke control embodying the invention.

Fig. 2 is a view of the parts in Fig. 1 taken at 90 thereto, parts beingbroken away and sectioned.

Fig. 3 is a detail section taken substantially on line 33 of Fig. 2 andshowing the choke valve fully opened.

Fig. 4. is a section similar to Fig. 3 but showing the choke valve fullyclosed by the thermostat.

Fig. 5 is an enlarged view of a portion of the structure in Fig. 1.

Figs. 1 and 2 show the upper air horn portion I of the mixture conduit 8of a downdraft carburetor. An unbalanced, butterfly, choke valve 9 ispivotally mounted in the air horn on a shaft I0 which projects laterallyinto a casing H carried at the side of the air horn. A cover i2 isadjustably and detachably secured to the casing by means of screws I3and clips I4 and has a central pintle I5 to which is secured the innerextremity of a bi-metal thermostat coil I5. A threaded fitting I'Iprojecting outwardly from the. center of the casing cover provides forattachment of a tube leading to a source of heat supply (not shown). Ifdesired, a suction connection may be provided between the thermostatcasing and the mixture conduit for drawing hot air therethrough, asdisclosed in Cofiey Patent No. 2,085,351.

An arm 20 is rigidly secured to the end of the choke shaft I0 withincasing I and has a finger 2i projecting through an arcuate slot 22 in abaiiie plate 23 which separates the casing and cover portions. Forfurther description of the structure and operation of these portions ofthe automatic choke control, reference is made to the above mentionedparent application.

Also secured to central pintle I5 on the thermostat casing cover is aflat, coiled bumper spring 24 which lies between the thermostat andcover I 2 and has its outer extremity extending through an eye 25 on thecover I2 and then bent inwardly, as at 26 (Fig. 2) so as to lie in thepath of hooked, outer extremity 2! of the thermostat coil. This latterhook is disposed, upon cooling and consequent unwinding of thethermostat, to engage finger 2l on choke shaft arm 20 and urge the chokevalve closed, as in Fig. 4. The thermostatic action is opposed by thedirect action of air flow on the unbalanced choke.

During the closing movement of the choke valve, under the influence ofthe thermostat, thermostat hook 2'! in passing eye 25, engages finger 26on bumper spring 24 so that further unwinding of the thermostat andclosing of the choke is resisted by the bumper spring. Eye 25 maintainsthe bumper spring in a prestressed condition so that its efiect inretarding the closing influence upon the choke valve, as exerted by thethermostat, is felt immediately that the bumper spring is picked up bythe thermostat. Thus, the bumper spring opposes with appreciable forcethe last portion of the choke-closing action of the thermostat.Preferably, the strength of spring 24 and the thermostat are adjusted sothat the thermostat will fully close the choke valve against spring 24only when the temperature is from 10 to 20 lower than that at which thechoke would be closed by the thermostat if spring 24 were omitted.

The invention is of especial advantage in case the engine is stoppedbefore being fully heated and when the outside temperature is very low.In such case, the thermostat may cool faster than the engine. To preventsuch excessive expansion of the thermostat and consequent closing of thechoke valve, spring 24 counteracts the portion of the thermostaticaction which causes the last 10-30" of choke closing movement. Eye 25insures proper pre-stressing of this spring which, thus, has acontrolled efiect on a relatively small portion of the thermostaticaction and exerts no force whatever upon the choke valve itself or whenthe thermostatic hook passesover eye v25 as the thermostat Winds uponitself during warm up. When the thermostat is fully heated, the chokevalve hangs fully openand hook 21 leaves finger 2|, as in Fig.3.

The bumper spring feature may be applied to substantially any type ofautomatic choke control utilizing a thermostat wherein it is desired toretard the thermostatic action or a portion thereof. The particular formof the bumper spring, as shown, is not essential and the exact portionof the thermostatic action effected there-' by may be modified asrequired. The invention may'be modified in these and other respects aswill occur to those skilled in the art and the exelusive use of allmodifications as come within the scope of the appended claims iscontemplated.

I claim: 1. In a carburetor, a'mixture conduit having a chokevalve-therein, an arm movable with said choke valve, a coiledthermostatic spring having an end portion for engaging said arm when thetemperature is low, to urge said choke valve -closed,.and a .prestressedspring positioned to be engaged by said end portion of said thermostaticspring during its action to effect the last part of the closing movementof-said choke valve for ophigh temperatures.

2. In a carburetor, a mixture conduit having a butterfly choke valvetherein, an arm rigid with the choke shaft outside said conduit, athermostatic coil spring mounted adjacent said arm and having a hookedouter'extremity forming a oneway operative connection therewith forurgin said choke valve closed when the temperature is low, and anadditional coiled spring mounted adjacent said thermostat and having aturned over end for engagement by the hooked end of said thermostatduring the portion of the thermostat action which effects the last partonly of the choke closing movement for opposing said part of thethermostat action.

3. A-carburetor as described in claim 2 in which the center of saidsecond coiled spring is permanently mounted and further including a stopelement for cooperating with the turned-over outer end of said secondspring to maintain the same in prestressed condition so as to be pickedup by said thermostat hooked end during the choke closing actionthereof.

4. In an automatic choke control for a carburetor, a casing having apintle projecting from a Wall thereof, a thermostatic coil centrallysecured to said pintle, and a bumper spring also secured to said pintlewith a portion disposed in the path of movement of the choke operativeouter portion of said thermostat so as to resist a portion of thethermostat action.

LEONARD D. BOYCE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,162,296 Chappell June 13, 1939 2,237,732 Giesler Apr. 8,1941 2,361,132 Smith Oct. 24, 1944 2,402,361 Bickwell June 18, 19462,410,758 Thompson Nov. 5, 1946

